.app_main{
  display: flex;
  flex-direction: row;
  height: 100vh;
  background-color: #f3f3f3;
}
.app_main .nav_bar{
  width: 256px;
  border-right: 1px solid #e4e4e4;
  background-color: #293348;
}
.app_main .main_body{
  flex: 1;
  margin-left: 20px;
  padding: 20px 0;
  background-color: #fff;
  box-sizing: border-box;
  overflow-y: scroll;
}